Current helmet manufacturing techniques involve using flat sheets of fabric from which a three-dimensional shape is formed. Numerous plies of the fabric, or preforms, are compressed together in a matched die mold that corresponds to the desired three-dimensional shape of the helmet. To try to achieve uniform thickness in a molded article that has a rounded shape, it is often necessary to introduce numerous cuts, darts, folds, wrinkles or irregularly-shaped patches into what would otherwise be a flat piece of fabric. This reduces ballistic resistance in the product helmet.
Other efforts to manufacture a helmet have involved rotating regions that are overlapped, as the assembly of preforms is built up with each additional ply of fabric, in order to distribute the extra thickness of the overlapped regions evenly about the preform assembly and theoretically achieve uniform thickness in the final molded product. This approach is sometimes capable of achieving a near-net-shape preform assembly, which has relatively good conformability to the final helmet shape with minimal wrinkling, but not at a desirable level of efficiency and consistency.
Cheese (U.S. Pat. No. 7,228,571) discloses a helmet manufactured by cutting rectangular blanks from a sheet of fabric and making cuts in each blank to form a crown portion. The blanks are stacked and molded to form the helmet. Each blank has four curved cuts extending inwardly, one from each side of the rectangle. Portions of the preform overlap other portions around the cuts.
Medwell (U.S. Pat. No. 4,656,674) discloses a helmet manufactured by cutting a preform along a zig-zag line so that each part has one straight edge and one edge with a series of teeth. The cut length is wound in several layers around a cylindrical former, so that the teeth of successive layers are alternating. The layers are then compressed to bend over the teeth and give a rigid preform.
A need nevertheless remains for methods for making a helmet in which the thickness of the helmet is more uniform, in which seams in the preform are minimized, and in which the ballistic resistance of resulting helmet is increased.